The present invention relates to a communications antenna. More specifically, this invention relates to a circularly polarized notch antenna with a single point feed, a low radar cross section, and a broad band frequency range suited for land, sea; air and spacecraft use.
Antennas are commonly employed to transmit, receive, enhance or ensure the reception of a signal within a desired frequency range depending upon the particular antenna design and specific application. Such signals are often transmitted and received at frequencies commonly employed to transmit audio and video signals. While present day antennas have generally proven to be satisfactory for their given applications, each often has limitations which limit its use in some manner.
One limitation with many present day antennas used on aircraft is their inability to maintain stealth, or in other words, to remain undetectable by radar. Maintaining stealth is particularly important with regard to certain military aircraft applications. In order to help maintain aircraft stealth, the Radar Cross Section (RCS) of an aircraft becomes important. RCS is a measure of the radar reflection characteristics of a target, or comparatively, a measure of the cross section of the sphere that would reflect the same energy back to a radar system irradiating the target if the sphere were substituted. As RCS increases, the integrity of aircraft stealth decreases and the aircraft becomes vulnerable to detection by radar. Therefore, it is highly desirable for certain military aircraft to maintain stealth by having a low RCS.
Another limitation of antennas used on most vehicles and with many land installations relates to the physical presence that most antennas must have in order to effectively transmit and receive signals. Most antennas must be exteriorly mounted on a vehicle or land based structure, or otherwise mounted to provide a relatively unobstructed transmission path to a receiver or transmitter. This requirement greatly limits antenna mounting locations, especially for military aircraft applications, and also greatly increases the RCS of the vehicle or aircraft, thus jeopardizing the ability of the vehicle or aircraft to operate undetected by a radar system.
Yet another limitation of antenna installations on military aircraft for electronic warfare transmission includes the number of antenna feed points. An antenna feed point is a point on an antenna where an electrical feed line couples to the antenna to transmit and receive RF signals within the frequency band that the antenna is designed to transmit and receive. Many modern antennas have dual feed points. The number of feed points directly contributes to the complexity of the antenna, its overall manufacturing cost and antenna utilization for a given application.
Still another limitation of antennas is their inability to transmit in a circularly polarized fashion. Many antennas, by the nature of their design, are capable of transmitting and receiving frequencies in a vertically or horizontally polarized fashion, but not circularly. Circular polarization is desirable in most transmissions related to military aircraft communications.
The problem of maintaining an aircraft""s stealth with regard to antennas has been addressed by the prior art by designing antennas capable of providing a low RCS. A crossed notch antenna is a type of antenna that is capable of providing a low radar cross section. However, a crossed notch antenna utilizes multiple feed points. Additionally, the problem of reducing the number of antenna feed points has been addressed by the prior art with the traditional horn antenna which commonly has a single feed point. However, horn antennas traditionally have a high radar cross section which jeopardizes aircraft stealth. Finally, the problem of transmitting a signal in a circularly polarized fashion has been addressed by the prior art with the crossed notch antenna. However, with a cross notched antenna, an additional external phase shift network is required to create the desired circular polarization.
What is needed then is an antenna that does not suffer from the above limitations. Ideally, such an antenna will provide for a single feed point that eliminates the problem of high RCS, and will thus provide a device that is capable of maintaining a low RCS thereby permitting an aircraft or other vehicle to maintain stealth. Additionally, such an antenna would be able to communicate using horizontal, vertical and circulating polarized signals without the need for an external phase shift network. This will permit savings with respect to antenna manufacturing assembly time, antenna installation time, and will provide an overall less complex antenna design.
In accordance with the teachings of the present invention, a circularly polarized notch antenna is disclosed. The invention provides an antenna with a planar polarizing member and multiple non-planar fins coupled to opposing polarizer sides. The invention also provides an electrical connection assembly that connects to the fins to communicate RF signals using a broad band of frequencies.
In one preferred embodiment, a circularly polarized notch antenna adaptable for use on land, sea, air and space vehicles includes a planar polarizing member, dual non-planar fins that are mechanically coupled to the polarizer, and a connection assembly that provides electrical connection to the antenna. The planar polarizing member is preferably square or rectangular,. manufactured from a dielectric material such as plastic or ceramic, and includes an elongated center slot. The fins are non-planar, preferably formed so as to include a ninety degree angle, and attached to opposing sides of the polarizing member. Additionally, each fin includes at one end at least one tuning slot, and at the other end dual curved edges formed by a notch, beginning at a fin interior and leading to a fin exterior. The connection assembly is typically a coaxial cable with an end coupler. In a dual, opposing fin arrangement, the outer conductor of the coaxial cable makes contact with one fin and the inner coaxial cable wire makes contact with the remaining fin. The cable passes through the elongated polarizer slot to facilitate the connection.
When the antenna parts are assembled, part reduction, overall antenna size and part complexity advantages are realized by eliminating the parts associated with an external phase shift network-and multiple feed cables or lines. Additionally, the notch antenna design of the present invention enhances electronic performance by communicating over a broader frequency range than traditional antennas.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.